1. Field of the Invention
The present invention generally relates to a kind of power module package structure. In particular, the present invention relates to a kind of power module package with characteristics of high heat dispersion efficiency and high integration.
2. Brief Description of the Prior Art
Increasing device complexity but shrinking size is common trend of the electrical product. Therefore, in addition to the shrinking size of the electrical product, how to put the most of electrical elements and wire bonds into the semiconductor package of the electrical product is very important. However, lots of heat is produced by the package structure with the high integration of electrical elements and wire bonds, when the electrical products are working. Especially for the power module, the heat affects the life and performance of the electrical product. Therefore, it is an important subject to improve the heat dispersion of the package structure with high integration of electrical elements and wire bonds.
Referring to FIG. 1, it is a cross-sectional diagram illustrating a conventional package structure of a power module. The package structure includes a high thermal conduction substrate 100, which is made of a high polymer isolating layer and an aluminum foil layer. All circuits of the package structure (not shown in the diagram) are fabricated on the substrate 100. The power element 110a, the control element 110b and other elements 110c are disposed on the substrate 100. A lead frame 121, 122 is suspended above the substrate 100 and several wire bonds 111, 112, 113 are formed to electrically connect the elements 110a, 110b, 110c and the circuits on the substrate 100. Then the elements and the circuits on the substrate 100 are encapsulated by package material, like resin, or molding but not the leads of lead frame 121, 122. The advantages of this power module package structure are simple and easy to manufacture. In this power module package structure, all elements 110a, 110b, 110c and all circuit are disposed on the substrate 100, and therefore the density of the circuits can not to be increased. So this package structure needs a bigger substrate, and it's cost is higher because it's bigger substrate. The heat which is produced by the power element 110a is transmitted to the heat sink through the substrate. And the heat is transmitted from the power element to the substrate by the adhesive between the substrate and the power element. Therefore, even the substrate is made of a high thermal conduction material but the large number of the heat can be transpired immediately.
Referring to FIG. 2, it is a cross-sectional diagram illustrating another conventional package structure of a power module. The power module package structure is similar to the package structure illustrated in FIG. 1. The structure also includes a high thermal conduction substrate 100, which is made of a high polymer isolating layer and an aluminum foil layer, with all circuits on it. The power element 110a, the control element 110b and other elements 110c are also disposed on the substrate 100. A lead frame 121, 122 is also suspended above the substrate 100 and several wire bonds 111, 112, 113 are also formed to electrically connect the elements 110a, 110b, 110c and the circuits on the substrate 100. And the elements and the circuits on the substrate 100 are also encapsulated by package material, like resin, or molding but not the leads of lead frame 121, 122. The difference between the package structure illustrated in FIG. 1 and FIG. 2 is that there is a metal plate 200 connected to the rear of the substrate 100 in the structure illustrated in FIG. 2. The advantages of this power module package structure are simple and easy to manufacture. And another advantage is that lots of heat can be immediately transmit by the metal plate 200 because it's high thermal conduction. Although there are many advantages of this package structure in FIG. 2, but the density of the circuits still can not be increased because all circuits are fabricated on the substrate 100. So the cost of the power module package still can be reduced.
Referring to FIG. 3, it is a cross-sectional diagram illustrating yet another conventional package structure of a power module. The package structure also includes a high thermal conduction substrate 100 which is made of a high polymer isolating layer and an aluminum foil layer. But the package structure in FIG. 3 is different from the package structure in FIG. 1 and in FIG. 2. In the power module illustrated in FIG. 3, all of the power element 110a and control element 110b are disposed on the lead frame by soldering or other method. The lead frame 121 and 122 are suspended above the substrate 100 but separated to each other without connecting. There are several wire bonds 111, 112 and etc. formed by wire bonding to electrically connect the elements 110a, 110b, lead frame 121, 122 and the circuits on it. And the elements and the circuits on the substrate 100 are encapsulated by package material, like resin, or molding but not the leads of lead frame 121, 122. The advantages of the power module package structure illustrated are simple and easy to manufacture. The density and accuracy of the circuits and package structure are limited because the circuits are fabricated on the lead frame. The heat produced by the power element 110a in power module is transmitted from the lead frame to substrate 110 through the packaging material. But the heat is not transmitted very well. It is because the heat is still transmitted from substrate to heat sink through the adhesive, and the adhesive is not a good thermal conductor.
Therefore, it is an important subject that how to improve the density of the package structure and to cost down. And it is another subject that how to solve the question of bad thermal conduction caused by the power element and the package structure with high density.